Display screen or portion thereof with a transitional graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a transitional graphical user interface showing the new design in a first position of a transitional sequence.

FIG. 2 is a front view of the display screen or portion thereof with a transitional graphical user interface showing the new design in a second position of the transitional sequence.

FIG. 3 is a front view of the display screen or portion thereof with a transitional graphical user interface showing the new design in a third position of the transitional sequence.

FIG. 4 is a front view of the display screen or portion thereof with a transitional graphical user interface showing the new design in a fourth position of the transitional sequence.

FIG. 5 is a front view of the display screen or portion thereof with a transitional graphical user interface showing the new design in a fifth position of the transitional sequence; and,

FIG. 6 is a front view of the display screen or portion thereof with a transitional graphical user interface showing the new design in a sixth position of the transitional sequence.

Within the drawings, the dashed lines show portions of the display screen or portion thereof with a transitional graphical user interface that form no part of the claimed design.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-6. The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a transitional graphical user interface, as shown and described. 